Prior to the present invention, the efficiency of stem cells to populate the germline and to produce non-human animals has been a major challenge, and there has been a continuing need for methods and compositions for the production of non-human animals from stem cells, including production of genetically modified non-human animals from genetically modified stem cells. This invention provides methods and compositions to produce non-human host embryos having a receptive niche for the development of donor stem cells, including genetically modified donor stem cells, into germ cells and gametes.